Vibrating meters, such as for example, vibrating densitometers and Coriolis flow meters are generally known, and are used to measure mass flow and other information related to materials flowing through a conduit in the vibratory meter. Exemplary Coriolis flow meters are disclosed in U.S. Pat. Nos. 4,109,524, 4,491,025, and Re. 31, 450. These vibratory meters have meter assemblies with one or more conduits of a straight or curved configuration. Each conduit configuration in a Coriolis mass flow meter, for example, has a set of natural vibration modes, which may be of simple bending, torsional, or coupled type. Each conduit can be driven to oscillate at a preferred mode. When there is no flow through the flowmeter, a driving force applied to the conduit(s) causes all points along the conduit(s) to oscillate with identical phase or with a small “zero offset”, which is a time delay measured at zero flow.
As material begins to flow through the conduit(s), Coriolis forces cause each point along the conduit(s) to have a different phase. For example, the phase at the inlet end of the flowmeter lags the phase at the centralized driver position, while the phase at the outlet leads the phase at the centralized driver position. Pickoffs on the conduit(s) produce sinusoidal signals representative of the motion of the conduit(s). Signals output from the pickoffs are processed to determine the time delay between the pickoffs. The time delay between the two or more pickoffs is proportional to the mass flow rate of material flowing through the conduit(s).
A meter electronics connected to the driver generates a drive signal to operate the driver and also to determine a mass flow rate and/or other properties of a process material from signals received from the pickoffs. The driver may comprise one of many well-known arrangements; however, a magnet and an opposing drive coil have received great success in the flowmeter industry. An alternating current is passed to the drive coil for vibrating the conduit(s) at a desired conduit amplitude and frequency. It is also known in the art to provide the pickoffs as a magnet and coil arrangement very similar to the driver arrangement.
Entrained gas is a common application problem for Coriolis flow meters. Improvements have been made to flow meters that improve performance in the presence of gas. These include improved alarm handling, better signal processing and noise rejection, wider mode separation, etc. However, accurate multiphase measurement may still be problematic due to three main error mechanisms—fluid decoupling, velocity of sound (VOS) effects, and asymmetric damping. It may not be possible to compensate for these error mechanisms without specific knowledge of parameters including bubble size, void fraction, liquid viscosity, speed of sound, and pressure. Flow profile effects are another area of concern for all types of flow meters, including large Coriolis flow meters. When Reynolds number is low, typically due to high viscosity, there are flow profile-related effects, which cause a reduction in sensitivity in Coriolis flow meters. Larger meters, which have a smaller tube length to tube diameter ratio, are more adversely affected. Larger meters also require thicker tube walls to contain high-pressure fluids. Accordingly, there is a need for flow tubes with a smaller tube length to tube diameter ratio and flow meters that can accurately measure a flow rate of a fluid. Such solutions can be realized with a multi-channel flow tube.